The present invention relates to a mold closing device for an injection molding machine, and more particularly to a mold closing device for producing large high-precision multi-component plastic parts.
Mold closing devices are known in the art. For example, British Pat. No. GB 2 300 142 describes a mold closing device, wherein each of the two outer mold mounting plates is made of one mold mounting plate that is fixedly secured to the machine frame and another mold mounting plate that is movably supported on the machine frame. The center mold carrier element is also movably supported on the machine frame by way of a supporting frame. Because the center mold carrier element which is rotatably arranged in the supporting frame is moveable, this component is relatively unstable, so that typically only lightweight mold halves can be placed on the mold mounting areas of the rotatable mold carrier element. Since the center mold carrier element and the moveable outer mold mounting plate represent two successively arranged moveable mold carrying units, the large tolerances render the mold closing unit very inaccurate, whereby the parallelism between the plates and the stationery outer mold mounting plate which is stationary in the machine frame is difficult to maintain.
Another type of mold closing device is known from German patent publication no. DE 197 33 667, which includes a stationary and a moveable mold mounting plate and a mold half carrier which is supported in support blocks that are moveable relative to the moveable mounting plate and rotatable about a vertical axis. The moveable mold mounting plate and the mold half carrier can be moved towards the stationery mold mounting plate so as to provide a closing pressure when a thermoplastic plastic is injected. This device disadvantageously also suffers from the relative instability of the device due to the large tolerances, as described above with reference to British patent publication no. GB 2 300 142.
German Pat. No. DE 36 20 175 describes an injection molding machine with at least two plasticizing and injection units as well as a stationary mold mounting plate and a moveable mold mounting plate that is guided by stationary tie bars. Each of stationary tie bars carries one set of the mold halves of injection molding molds. A prismatic core carrying body is arranged between the stationary tie bars which can rotate about its axis and is displaceable in the direction of the stationery tie bars. The axis-parallel side faces of the core carrying body include the other set of mold halves of the injection molding molds. This core carrying body is actually not supported on the machine bed, but is held only by tie bars that are movably supported on the moveable mold mounting plate. In other words, only the core carrying bodies and the associated mold halves which are lightweight are operational. This particular support structure of the core carrying body relative to the moveable mold mounting plate, which is not supported on either the machine bed or the tie bars used for the closing motion, causes the device to be particularly unstable and hence has all the disadvantages described above with reference to British patent publication no. GB 2 300 142.
A tie bar pulling device for a 2-platen or 3-platen injection molding machine is described in German patent publication no. DE 197 10 412, wherein the tie bars extend through two mold mounting plates which each carries a corresponding mold half. When the mold is opened, the tie bars are pulled out of one mounting plate with which they are interlocked in the closed state, allowing access to the space between the mold mounting plates. This device, unlike the present invention, is directed to an injection molding machine without a turning device for the mold, which makes it difficult to produce multi-component injection molded parts.
German Pat. No. DE 196 50 854 describes a method and a device for producing multilayer plastic parts, whereby a plastic injection molded part is coated with at least one layer of 2-component Thermosetting plastics and the two components are injection-molded successively in a synchronous cycle in the same mold. For this purpose, a baseplate is used which supports two mold halves that are arranged side-by-side and rotatably supported for rotation about a horizontal longitudinal machine axis. Female molds of an injection molding machine and a RIM device are arranged opposite to the mold halves. After injecting thermoplastic material with the injection molding machine, the baseplate is rotated by 180°. In the following cycle, a new thermoplastic part is molded while the part produced in the preceding cycle is coated with the 2-component Thermosetting plastics. With this device, both injection molding devices are disadvantageously located on the same side of the machine, which poses significant problems at the installation side and for the operation of the injection molding devices. Moreover, this device is suitable only for producing small plastic parts, since the two mold halves could otherwise not be arranged side-by-side. It is not clear from the description how a baseplate that is rotatable about the longitudinal mold axis can be fixedly connected with the female molds of the injection molding machine and the RIM device, which leaves unanswered the question concerning the accuracy of the mold fit and the availability of a sufficiently high closing pressure.
It would therefore be desirable and advantageous to provide a mold closing device with an improved stability, which obviates prior art shortcomings and is able to specifically produce large high-precision multi-component plastic parts.